Transforming Equations into Systems

[hbomb]

Could someone give a brief run down of how to transform a given equation into a system of first order equations. Example: u"+.5u'+2u=0

How do you transform a given system of equations into a single equation of second order. Example: x1'=3x1-2x2 , x2'=2x1-2x2

Thanks a bunch, because my book doesn't show clearly how to do this.

 

[arildno]

Set x=u', for example.